1. Field of the Invention
The present invention relates to a method of making a group III-V compound semiconductor wafer, and more particularly, it relates to a method of making a group III-V compound semiconductor wafer having an epitaxial layer grown by vapor-phase epitaxy.
2. Description of the Prior Art
The recent development of optical communication has caused an increase in the production quantity of photodiodes and the like. For example, an InP photodiode (hereinafter referred to as a pin-PD) is prepared by growing an epitaxial layer on an indium-phosphorus (hereinafter referred to as (InP) substrate by chloride vapor-phase epitaxy.
In order to prepare a pin-PD, an InP substrate is formed by cutting an InP ingot into slices and chamfering and grinding and polishing each slice. Then, a group III-V compound layer is epitaxially grown on this substrate for preparing an InP wafer, and thereafter a Zn diffusion layer, a protective film and the like are formed on this InP wafer. While the InP wafer grown into a diameter of two inches is generally cut into a rectangular form and thereafter sub-jected to a device process of forming the Zn diffusion layer and the like, such a wafer has recently been subjected to the device process in the circular shape of 2 inches in diameter as such, in order to reduce the cost.
An end portion of the InP wafer, which is generally picked up and carried with tweezers or held by a conveying machine, may be chipped or cracked in the device process. In order to prevent this, the end portion of the substrate is generally chamfered. For example, Japanese Utility Model Laying-Open No. 58-103144 (1983) describes a technique of forming a prescribed chamfered part on an end portion of a GaAs substrate for preventing flaws in mirror grinding or chipping in step movement.
On the other hand, Japanese Patent Laying-Open No. 6-61201 (1994) discloses a technique of forming a prescribed chamfered part on an end portion of a silicon substrate for preventing occurrence of edge crowns.
When a wafer prepared by growing an epitaxial layer on an InP substrate provided with a chamfered portion is subjected to a device process, however, the wafer is disadvantageously cracked in a diffusion step for impurity introduction, a thermal CVD step for forming a protective film or an ultrasonic cleaning step for removing foreign matter.